The mitral valve and tricuspid valve are unidirectional heart valves that separate the atria left and right respectively, from the corresponding heart ventricles. These valves have a distinct anatomical and physiological structure, having two (mitral) or three (tricuspid) sail-like leaflets connected to a subvalvular mechanism of strings (chordae tendinae) and papillary muscles forming a part of the heart's ventricular shape, function and size.
The heart has four chambers: the right and left atria, and the right and left ventricles. The atria receive blood and then pump it into the ventricles, which then pump it out into the body.
The synchronous pumping actions of the left and right sides of the heart constitute the cardiac cycle. The cycle begins with a period of ventricular relaxation, called ventricular diastole. The cycle ends with a period of ventricular contraction, called ventricular systole.
The heart has four valves that ensure that blood does not flow in the wrong direction during the cardiac cycle; that is, to ensure that the blood does not back flow from the ventricles into the corresponding atria, or back flow from the arteries into the corresponding ventricles. The valve between the left atrium and the left ventricle is the mitral valve. The valve between the right atrium and the right ventricle is the tricuspid valve. The pulmonary valve is at the opening of the pulmonary artery. The aortic valve is at the opening of the aorta.
The opening and closing of heart valves occur primarily as a result of pressure differences. For example, the opening and closing of the mitral valve occurs as a result of the pressure differences between the left atrium and the left ventricle. During ventricular diastole, when ventricles are relaxed, the venous return of blood from the pulmonary veins into the left atrium causes the pressure in the atrium to exceed that in the ventricle. As a result, the mitral valve opens, allowing blood to enter the ventricle. As the ventricle contracts during ventricular systole, the intraventricular pressure rises above the pressure in the atrium and pushes the mitral valve shut.
As noted above, these valves feature a plurality of leaflets connected to chordae tendinae and papillary muscles, which allow the leaflets to resist the high pressure developed during contractions (pumping) of the left and right ventricles.
In a healthy heart, the chords become taut, preventing the leaflets from being forced into the left or right atria and everted. Prolapse is a term used to describe the condition wherein the coaptation edges of each leaflet initially may co-apt and close, but then the leaflets rise higher and the edges separate and the valve leaks. This is normally prevented by contraction of the papillary muscles and the normal length of the chords. Contraction of the papillary muscles is simultaneous with the contraction of the ventricle and serves to keep healthy valve leaflets tightly shut at peak contraction pressures exerted by the ventricle.
Valve malfunction can result from the chords becoming stretched, and in some cases tearing. When a chord tears, the result is a flailed leaflet. Also, a normally structured valve may not function properly because of an enlargement of the valve annulus pulling the leaflets apart. This condition is referred to as a dilation of the annulus and generally results from heart muscle failure. In addition, the valve may be defective at birth or because of an acquired disease, usually infectious or inflammatory.
Diseases of the valves can cause either narrowing (stenosis) or dilatation (regurgitation, insufficiency) or a combination of those, of the valve. Surgical treatment for repair or replacement of the valves includes an open-heart procedure, extracorporeal circulation and, if replaced, a complete resection of the diseased valve.
Currently all available surgical options for valve replacement involve open heart surgery; although minimally invasive methods for valve replacement are more desirable, such methods are still in the experimental stage.
Even valves which could theoretically be provided through a non-invasive method, such as those taught by U.S. Pat. No. 7,381,220, have many drawbacks. For example, the taught valves are useful for replacement of the existing valves; however, their installation through non-invasive means is problematic. Furthermore, the valves themselves, even when installed in a manner that supports existing valve tissue, must still withstand very high pressures. Such high pressures can lead to many different types of problems, including reflux as blood returns through heart in a retrograde manner.
It may be desirable to provide a valve prosthesis that supports the mitral and/or tricuspid valve without necessarily replacing it, but instead supplements the native valve functionality by providing an adjunctive valve prosthesis, which cooperates together with the native valve for improved functionality. The background art also does not teach or suggest such a valve prosthesis which may optionally be inserted through minimally invasive surgical techniques.